Nutrient Cycling in a Stand of Acacia holosericea A. Cunn. Ex G. Don. II. Phosphorus and Endomycorrhizal Associations

Abstract

The cycling of phosphorus was studied in a 3-year-old plantation of Acacia holosericea (1111 trees ha-1). Over a 13-month period, the gross demand by the plantation for phosphorus was estimated to be 1260 g ha-1. Of this, 17% was supplied through biochemical cycling within the plants and the balance was obtained from the soil. Of the total phosphorus in the phyllodes, approximately 85% was remobilized into the tree before phyllode fall. A total of 148 g P ha-1 was estimated to be cycled in litter over the study period. Topsoil samples collected from several points within the Eucalyptus tetrodonta open-forest contained three mycorrhizal Endogone spore types. Type GE1 appeared to be a strain of Gigaspora gilmoreii, type GE2 was an undescribed Gigaspora species and type GE3 was similar to Gigaspora gigantea. Only one sporocarpic Endogone species was found which was similar to Sclerocystis coremioides. Type GE1 was the dominant type in the E. tetrodonta open-forest and significantly greater numbers of it occurred around the roots of native legumes in a survey which included Brachysema uniflora, Calopogonium mucunioides, Galactia tenuiflora, Acacia aulacocarpa, A. holosericea, A. latescens, A. torulosa and A. yirrkallensis. All the plants examined except Eucalyptus tetrodonta, Calytrix laricina and Rhychelytrum repens were infected by vesicular-arbuscular mycorrhizal fungi. The results of this study suggest that the infection of plant species by mycorrhizal fungi is a prerequisite for successful long-term vegetation establishment on areas rehabilitated after mining.